Cassini's slant on the rings

Cassini's slant on the rings

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!

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[Click to embiggen.]

Oh, wow! This was taken when the spacecraft was almost in the plane of the rings, which are incredibly thin. You can see several different rings, including the broad A ring in the middle and the thin F ring on the outside. There are also two moons: Janus (the larger one, above) and Prometheus (smaller, below). Janus is about 180 km (110 miles) across, which isn't terribly big, but Prometheus is even smaller: 120 km (75 miles).

This picture made me smile not only because it is carved out of raw coolness, but also because it's the complement of an earlier image from Cassini (to the right). The earlier shot is of the moon Epimetheus, which shares an orbit with Janus, and Pandora, which shares an orbit with Prometheus! So the two images go together like a pair of gloves, each showing one of a pair of orbit-sharing moons.
Also, in the big image, take a look at the thin F ring: follow it from the far side to the near side. Just as you pass the bottom left and start moving to the upper right, do you see two spots where it appears thicker, like it's lumpy? Well, it is lumpy! Pandora and Prometheus are the ring's shepherd moons, using their gravity to keep the ring particles tightly in place. But when they pass any given point in the rings, their gravity leaves a wake behind, almost like a boat's wake. That deforms the ring a bit, and you can see that in this image as a thickening in the ring. The animation I've inserted here actually shows that as it happens.

Amazing, what can be seen in a single image from Saturn. Especially if you have other images to back it up.

I like this new image a lot. Hmmm, have I found my new desktop picture? Why yes, yes I have.